I would like to see a snippet of the campaign mode. Maybe a part of the first mission, just to get s feel for what it might end up being like. As for specific weapons, vehicles and what not; that's up to you!

A mission or two from the campaign would be good, but a multiplayer or firefight demo would last much longer AND may give you more feedbacks to improve the game. All in all, I would like to have what Jack said, part of the campaign (Since we've had a taste of firefight from that old build).

As with the weapons, here's a list:
- Assault Rifle/MA5B: 60-rounds magazine would be very helpful in this type of game.
- Battle Rifle/DMR: Any of those two, but again, the BR55 would be a close-medium range weapon while the DMR is a medium-long range weapon.
- Shotgun: Who doesn't want to go up close and personal to blast alien faces?
- SRS99D AM: The sniper is not as effective here as it is in FPSes, but it's still deadly!
- Pistol: Not a very important gun, but it's always handy and should be the gun you spawn with. Preferably the beastly M6D.
- SMG: Give that gun back to us, we haven't had the M7 since Halo 3: ODST!
- Plasma Pistol: No Halo game is complete without this.
- Plasma Rifle: Likewise... *Looks at Halo 4*
- Needler: Just the fun gun!
- Carbine: It has been a great gun since Halo 2!

The obvious Warthog, Ghost, and maybe the Banshee. Back to Halo: Combat Evolved's default eh?
Obviously Spartans (Which Spartan will depend on the story you've got for the campaign! You don't want to put in SPARTAN-IVs for a game set in the Human-Covenant War!), then the handy-dandy marines, grunts, elites, jackals.

Great list, and probably the easiest to obtain sounds for, I can add the Ghost and Banshee no problem, Warthog will be kind of glitchy if coded wrong, For the Spartan-IVs the armor for the Spartan is mainly a Firefight unlockable, but yes the Spartan will look like a later generation.

I forgot to mention that you'll want to avoid the warthog for the time being if it's anything but a part of the campaign. Also, the armor as an unlockable sounds great, another reason to play the game more!
And "but yes the Spartan will look like a later generation" does that mean that the story is set some time after the Reclaimer Trilogy era? Or any other time after Halo 4?